In many liquid dispensing systems, it is necessary to continuously recirculate the liquid in the system when the system is not in a dispensing mode. For example, in hot melt adhesive dispensing equipment employing multiple dispensing valves, it is often necessary to use two separate hydraulic valves for each stream of dispensed adhesive. These valves are typically mounted to a manifold with one being used to dispense liquid and the other being used to recirculate the liquid. The two valves operate in opposite phases or cycles and typically require separate activation signals. The dispensing valve applies adhesive to the substrate while the recirculation valve is closed and, when the dispensing valve is closed, the recirculation valve is opened to recirculate adhesive back to a supply tank.
Problems associated with dispensing systems such as described above therefore relate to the need for specialized recirculation plates and recirculation valves or modules mounted on the manifold. This is a particular problem both in terms of the added cost associated with the recirculation plates and valves or modules as well as the larger manifolds required to accommodate these additional components. Further, separate control of the dispensing and recirculation valves requires that timing considerations be taken into account. This may require additional timers and/or other control components.
Other valves exist which allow for both a dispensing and recirculation function to be performed by a single valve. However, these valves may require manual operation to changeover between a dispensing mode and a recirculation mode or may have various other drawbacks which limit their availability and practicality in many situations.
For these and other reasons and to solve various problems in this area of technology, it would be desirable to provide a liquid dispensing module that eliminates various extra recirculation components, allows for a reduced manifold size, and generally reduces the number of flow control components and costs typically associated with liquid dispensing and recirculating systems.